There are known electric power converters that receive multi-phase alternating-current from a commercial power source and output multi-phase alternating-current for variably driving the speed of an AC motor. For example, Japanese Published Patent Application No. 2002-354815 discloses an electric power converting apparatus, and in particular, a control method of a matrix converter for variably controlling a motor speed using three-phase alternating current as an input.
In that apparatus, it is known to generate a PMW pulse for operating the electric power converting apparatus. An input current command value is calculated from a phase of an input current, a positive-phase-sequence current component and a negative-phase-sequence current component. An input current distribution ratio is calculated from the input current command value. An input power factor is controlled in order to suppress an influence of phase unbalance of the input electric power. Input voltages are detected, and two line voltages are elected from a magnitude relation of the input voltages. Finally, the PWM pulse is calculated from the two line voltages and the input current distribution ratio.